The subject invention generally relates to an expansion device for use in an air conditioning system of a motor vehicle. More specifically, the subject invention relates to an expansion device that controls the flow of refrigerant to an evaporator of the air conditioning system.
Expansion devices e.g., thermostatic expansion valves (TXV) and orifice tubes, are known in the art. In fact, expansion devices have been utilized to regulate, i.e., control, flow of refrigerant in air conditioning systems for many years. As understood by those skilled in the art, in addition to the expansion device, the air conditioning systems also include a refrigerant compressor, a condenser, a receiver, and an evaporator.
The refrigerant is in a vapor or gaseous phase as it exits the evaporator. Another desirable functional feature in such an air conditioning system is the ability to limit the amount of refrigerant in the evaporator while the system is not operating, the evaporator being in the passenger compartment of the vehicle. In order to accomplish this function, it would be necessary to employ a shut-off valve to control flow to the evaporator.
Accordingly, the subject invention provides a unique expansion device that is able to perform the functions of refrigerant expansion, flow control, and shut-off.
An expansion device assembly includes a valve body having an axis and an inlet end and an outlet end with an orifice tube extending through the body for conveying refrigerant from an inlet pipe to an outlet pipe while expanding the refrigerant into the outlet pipe. A conical shaped valve seat forms an inlet to the orifice tube and flares radially outwardly. A plunger has a conical shaped valve end for engaging and sealing the conical valve seat to prevent refrigerant from entering the orifice tube. A rod extends axially from the valve end and a solenoid coil surrounds the rod for moving the valve end out of engagement with the valve seat.
The invention provides an orifice tube and a normally closed, solenoid activated, shut-off mechanism integrated into a single device that performs both refrigerant expansion during operation and shut-off during non-operating conditions. This is accomplished by adding a trumpet-like end to the orifice tube to serve as a valve-sealing surface when engaged by a plunger of complimentary design and dimensions that is solenoid activated. The motion of the plunger is linear and is retracted by the solenoid during system operation to allow flow of refrigerant and is moved to an closed position with the aid of a spring as the solenoid circuit is deactivated. The travel of the plunger is guided to the trumpet valve seat by the cage supporting the orifice tube filter screen.